Lowest temperatures are moving upward
To the editor:
During the coming week, the daily maximum minus night minimum is predicted to be between 6 and 10 °C. Mr. Schemine asks a question in his letter that possibly is on the minds of many readers: How can a few degrees of temperature make a difference, when we experience more change than that in a single day?
It does seem counterintuitive that 1 or 2 °C could make much of a difference. However, the experts are undoubtedly correct on this. The important point is that the 2 °C we are talking about is a difference in the planet’s average temperature. Every day is, on average, warmer. In fact, in a paper in Nature in November 2013, Mora et al. analyze the full complement of climate models available to determine at what date the lowest temperature expected at a location will exceed the maximal temperature at that location in the interval between 1880 and 2005. Their best mean date for this to occur is 2047, just a little over 30 years from now. Some locations will experience this change as soon as 2020.
It is also interesting for people thinking as Mr. Schemine does to know that the Little Ice Age mean global temperature was only about 1 °C lower than historic measured temperatures of last century.
Already many species of animals and plants are moving their habitat; the change in average temperature is currently proceeding much, much faster than any record in Earth’s history except for the Permian-Eemian Thermal Maximum. Animals can move easily, but plants are not very mobile. In a paper by Burrows et al. in Science magazine in 2011, the authors write that the “median velocity of isotherms across the ocean (21.7 km/decade) is 79 percent of that on land (27.3 km/decade), but when comparing only those latitudes where both land and ocean are present (50°S to 80°N), velocities in the ocean (27.5 km/decade) are similar to those on land (27.4 km/decade).”
These authors also point out that spring temperatures are advancing by more than a day per decade. The growing season is getting longer in Ohio, and we were recently reclassified into another plant hardiness zone.
These effects are real, even if the difference in mean temperature is small.
This is a case in which intuition fails to help us understand what’s happening. The experts are really experts, and are correct.
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